llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_allocator.h

//===-- sanitizer_allocator.h -----------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Specialized memory allocator for ThreadSanitizer, MemorySanitizer, etc.
//
//===----------------------------------------------------------------------===//

#ifndef SANITIZER_ALLOCATOR_H
#define SANITIZER_ALLOCATOR_H

#include "sanitizer_internal_defs.h"
#include "sanitizer_common.h"
#include "sanitizer_libc.h"
#include "sanitizer_list.h"
#include "sanitizer_mutex.h"

namespace __sanitizer {

// SizeClassMap maps allocation sizes into size classes and back.
// Class 0 corresponds to size 0.
// Classes 1 - 16 correspond to sizes 8 - 128 (size = class_id * 8).
// Next 8 classes: 128 + i * 16 (i = 1 to 8).
// Next 8 classes: 256 + i * 32 (i = 1 to 8).
// ...
// Next 8 classes: 2^k + i * 2^(k-3) (i = 1 to 8).
// Last class corresponds to kMaxSize = 1 << kMaxSizeLog.
//
// This structure of the size class map gives us:
//   - Efficient table-free class-to-size and size-to-class functions.
//   - Difference between two consequent size classes is betweed 12% and 6%
//
// This class also gives a hint to a thread-caching allocator about the amount
// of chunks that need to be cached per-thread:
//  - kMaxNumCached is the maximal number of chunks per size class.
//  - (1 << kMaxBytesCachedLog) is the maximal number of bytes per size class.
//
// Part of output of SizeClassMap::Print():
//    c00 => s: 0 diff: +0 00% l 0 cached: 0 0; id 0
//    c01 => s: 8 diff: +8 00% l 3 cached: 256 2048; id 1
//    c02 => s: 16 diff: +8 100% l 4 cached: 256 4096; id 2
//    ...
//    c07 => s: 56 diff: +8 16% l 5 cached: 256 14336; id 7
//
//    c08 => s: 64 diff: +8 14% l 6 cached: 256 16384; id 8
//    ...
//    c15 => s: 120 diff: +8 07% l 6 cached: 256 30720; id 15
//
//    c16 => s: 128 diff: +8 06% l 7 cached: 256 32768; id 16
//    c17 => s: 144 diff: +16 12% l 7 cached: 227 32688; id 17
//    ...
//    c23 => s: 240 diff: +16 07% l 7 cached: 136 32640; id 23
//
//    c24 => s: 256 diff: +16 06% l 8 cached: 128 32768; id 24
//    c25 => s: 288 diff: +32 12% l 8 cached: 113 32544; id 25
//    ...
//    c31 => s: 480 diff: +32 07% l 8 cached: 68 32640; id 31
//
//    c32 => s: 512 diff: +32 06% l 9 cached: 64 32768; id 32


template <uptr kMaxSizeLog, uptr kMaxNumCached, uptr kMaxBytesCachedLog>
class SizeClassMap {
  static const uptr kMinSizeLog = 3;
  static const uptr kMidSizeLog = kMinSizeLog + 4;
  static const uptr kMinSize = 1 << kMinSizeLog;
  static const uptr kMidSize = 1 << kMidSizeLog;
  static const uptr kMidClass = kMidSize / kMinSize;
  static const uptr S = 3;
  static const uptr M = (1 << S) - 1;

 public:
  static const uptr kMaxSize = 1 << kMaxSizeLog;
  static const uptr kNumClasses =
      kMidClass + ((kMaxSizeLog - kMidSizeLog) << S) + 1;
  COMPILER_CHECK(kNumClasses >= 32 && kNumClasses <= 256);
  static const uptr kNumClassesRounded =
      kNumClasses == 32  ? 32 :
      kNumClasses <= 64  ? 64 :
      kNumClasses <= 128 ? 128 : 256;

  static uptr Size(uptr class_id) {
    if (class_id <= kMidClass)
      return kMinSize * class_id;
    class_id -= kMidClass;
    uptr t = kMidSize << (class_id >> S);
    return t + (t >> S) * (class_id & M);
  }

  static uptr ClassID(uptr size) {
    if (size <= kMidSize)
      return (size + kMinSize - 1) >> kMinSizeLog;
    if (size > kMaxSize) return 0;
    uptr l = SANITIZER_WORDSIZE - 1 - __builtin_clzl(size);
    uptr hbits = (size >> (l - S)) & M;
    uptr lbits = size & ((1 << (l - S)) - 1);
    uptr l1 = l - kMidSizeLog;
    return kMidClass + (l1 << S) + hbits + (lbits > 0);
  }

  static uptr MaxCached(uptr class_id) {
    if (class_id == 0) return 0;
    uptr n = (1UL << kMaxBytesCachedLog) / Size(class_id);
    return Max(1UL, Min(kMaxNumCached, n));
  }

  static void Print() {
    uptr prev_s = 0;
    uptr total_cached = 0;
    for (uptr i = 0; i < kNumClasses; i++) {
      uptr s = Size(i);
      if (s >= kMidSize / 2 && (s & (s - 1)) == 0)
        Printf("\n");
      uptr d = s - prev_s;
      uptr p = prev_s ? (d * 100 / prev_s) : 0;
      uptr l = SANITIZER_WORDSIZE - 1 - __builtin_clzl(s);
      uptr cached = MaxCached(i) * s;
      Printf("c%02zd => s: %zd diff: +%zd %02zd%% l %zd "
             "cached: %zd %zd; id %zd\n",
             i, Size(i), d, p, l, MaxCached(i), cached, ClassID(s));
      total_cached += cached;
      prev_s = s;
    }
    Printf("Total cached: %zd\n", total_cached);
  }

  static void Validate() {
    for (uptr c = 1; c < kNumClasses; c++) {
      // Printf("Validate: c%zd\n", c);
      uptr s = Size(c);
      CHECK_EQ(ClassID(s), c);
      if (c != kNumClasses - 1)
        CHECK_EQ(ClassID(s + 1), c + 1);
      CHECK_EQ(ClassID(s - 1), c);
      if (c)
        CHECK_GT(Size(c), Size(c-1));
    }
    CHECK_EQ(ClassID(kMaxSize + 1), 0);

    for (uptr s = 1; s <= kMaxSize; s++) {
      uptr c = ClassID(s);
      // Printf("s%zd => c%zd\n", s, c);
      CHECK_LT(c, kNumClasses);
      CHECK_GE(Size(c), s);
      if (c > 0)
        CHECK_LT(Size(c-1), s);
    }
  }
};

typedef SizeClassMap<21, 256, 16> DefaultSizeClassMap;
typedef SizeClassMap<15, 64, 14> CompactSizeClassMap;


struct AllocatorListNode {
  AllocatorListNode *next;
};

typedef IntrusiveList<AllocatorListNode> AllocatorFreeList;

// Move at most max_count chunks from allocate_from to allocate_to.
// This function is better be a method of AllocatorFreeList, but we can't
// inherit it from IntrusiveList as the ancient gcc complains about non-PODness.
static inline void BulkMove(uptr max_count,
                            AllocatorFreeList *allocate_from,
                            AllocatorFreeList *allocate_to) {
  CHECK(!allocate_from->empty());
  CHECK(allocate_to->empty());
  if (allocate_from->size() <= max_count) {
    allocate_to->append_front(allocate_from);
    CHECK(allocate_from->empty());
  } else {
    for (uptr i = 0; i < max_count; i++) {
      AllocatorListNode *node = allocate_from->front();
      allocate_from->pop_front();
      allocate_to->push_front(node);
    }
    CHECK(!allocate_from->empty());
  }
  CHECK(!allocate_to->empty());
}

// Allocators call these callbacks on mmap/munmap.
struct NoOpMapUnmapCallback {
  void OnMap(uptr p, uptr size) const { }
  void OnUnmap(uptr p, uptr size) const { }
};

// SizeClassAllocator64 -- allocator for 64-bit address space.
//
// Space: a portion of address space of kSpaceSize bytes starting at
// a fixed address (kSpaceBeg). Both constants are powers of two and
// kSpaceBeg is kSpaceSize-aligned.
// At the beginning the entire space is mprotect-ed, then small parts of it
// are mapped on demand.
//
// Region: a part of Space dedicated to a single size class.
// There are kNumClasses Regions of equal size.
//
// UserChunk: a piece of memory returned to user.
// MetaChunk: kMetadataSize bytes of metadata associated with a UserChunk.
//
// A Region looks like this:
// UserChunk1 ... UserChunkN <gap> MetaChunkN ... MetaChunk1
template <const uptr kSpaceBeg, const uptr kSpaceSize,
          const uptr kMetadataSize, class SizeClassMap,
          class MapUnmapCallback = NoOpMapUnmapCallback>
class SizeClassAllocator64 {
 public:
  void Init() {
    CHECK_EQ(kSpaceBeg,
             reinterpret_cast<uptr>(Mprotect(kSpaceBeg, kSpaceSize)));
    MapWithCallback(kSpaceEnd, AdditionalSize());
  }

  void MapWithCallback(uptr beg, uptr size) {
    CHECK_EQ(beg, reinterpret_cast<uptr>(MmapFixedOrDie(beg, size)));
    MapUnmapCallback().OnMap(beg, size);
  }

  void UnmapWithCallback(uptr beg, uptr size) {
    MapUnmapCallback().OnUnmap(beg, size);
    UnmapOrDie(reinterpret_cast<void *>(beg), size);
  }

  bool CanAllocate(uptr size, uptr alignment) {
    return size <= SizeClassMap::kMaxSize &&
      alignment <= SizeClassMap::kMaxSize;
  }

  void *Allocate(uptr size, uptr alignment) {
    if (size < alignment) size = alignment;
    CHECK(CanAllocate(size, alignment));
    return AllocateBySizeClass(ClassID(size));
  }

  void Deallocate(void *p) {
    CHECK(PointerIsMine(p));
    DeallocateBySizeClass(p, GetSizeClass(p));
  }

  // Allocate several chunks of the given class_id.
  void BulkAllocate(uptr class_id, AllocatorFreeList *free_list) {
    CHECK_LT(class_id, kNumClasses);
    RegionInfo *region = GetRegionInfo(class_id);
    SpinMutexLock l(&region->mutex);
    if (region->free_list.empty()) {
      PopulateFreeList(class_id, region);
    }
    BulkMove(SizeClassMap::MaxCached(class_id), &region->free_list, free_list);
  }

  // Swallow the entire free_list for the given class_id.
  void BulkDeallocate(uptr class_id, AllocatorFreeList *free_list) {
    CHECK_LT(class_id, kNumClasses);
    RegionInfo *region = GetRegionInfo(class_id);
    SpinMutexLock l(&region->mutex);
    region->free_list.append_front(free_list);
  }

  static bool PointerIsMine(void *p) {
    return reinterpret_cast<uptr>(p) / kSpaceSize == kSpaceBeg / kSpaceSize;
  }

  static uptr GetSizeClass(void *p) {
    return (reinterpret_cast<uptr>(p) / kRegionSize) % kNumClassesRounded;
  }

  void *GetBlockBegin(void *p) {
    uptr class_id = GetSizeClass(p);
    uptr size = SizeClassMap::Size(class_id);
    uptr chunk_idx = GetChunkIdx((uptr)p, size);
    uptr reg_beg = (uptr)p & ~(kRegionSize - 1);
    uptr beg = chunk_idx * size;
    uptr next_beg = beg + size;
    RegionInfo *region = GetRegionInfo(class_id);
    if (region->mapped_user >= next_beg)
      return reinterpret_cast<void*>(reg_beg + beg);
    return 0;
  }

  static uptr GetActuallyAllocatedSize(void *p) {
    CHECK(PointerIsMine(p));
    return SizeClassMap::Size(GetSizeClass(p));
  }

  uptr ClassID(uptr size) { return SizeClassMap::ClassID(size); }

  void *GetMetaData(void *p) {
    uptr class_id = GetSizeClass(p);
    uptr size = SizeClassMap::Size(class_id);
    uptr chunk_idx = GetChunkIdx(reinterpret_cast<uptr>(p), size);
    return reinterpret_cast<void*>(kSpaceBeg + (kRegionSize * (class_id + 1)) -
                                   (1 + chunk_idx) * kMetadataSize);
  }

  uptr TotalMemoryUsed() {
    uptr res = 0;
    for (uptr i = 0; i < kNumClasses; i++)
      res += GetRegionInfo(i)->allocated_user;
    return res;
  }

  // Test-only.
  void TestOnlyUnmap() {
    UnmapWithCallback(kSpaceBeg, kSpaceSize + AdditionalSize());
  }

  typedef SizeClassMap SizeClassMapT;
  static const uptr kNumClasses = SizeClassMap::kNumClasses;
  static const uptr kNumClassesRounded = SizeClassMap::kNumClassesRounded;

 private:
  static const uptr kRegionSize = kSpaceSize / kNumClassesRounded;
  static const uptr kSpaceEnd = kSpaceBeg + kSpaceSize;
  COMPILER_CHECK(kSpaceBeg % kSpaceSize == 0);
  // kRegionSize must be >= 2^32.
  COMPILER_CHECK((kRegionSize) >= (1ULL << (SANITIZER_WORDSIZE / 2)));
  // Populate the free list with at most this number of bytes at once
  // or with one element if its size is greater.
  static const uptr kPopulateSize = 1 << 18;
  // Call mmap for user memory with at least this size.
  static const uptr kUserMapSize = 1 << 18;
  // Call mmap for metadata memory with at least this size.
  static const uptr kMetaMapSize = 1 << 16;

  struct RegionInfo {
    SpinMutex mutex;
    AllocatorFreeList free_list;
    uptr allocated_user;  // Bytes allocated for user memory.
    uptr allocated_meta;  // Bytes allocated for metadata.
    uptr mapped_user;  // Bytes mapped for user memory.
    uptr mapped_meta;  // Bytes mapped for metadata.
  };
  COMPILER_CHECK(sizeof(RegionInfo) >= kCacheLineSize);

  static uptr AdditionalSize() {
    uptr PageSize = GetPageSizeCached();
    uptr res = Max(sizeof(RegionInfo) * kNumClassesRounded, PageSize);
    CHECK_EQ(res % PageSize, 0);
    return res;
  }

  RegionInfo *GetRegionInfo(uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    RegionInfo *regions = reinterpret_cast<RegionInfo*>(kSpaceBeg + kSpaceSize);
    return &regions[class_id];
  }

  static uptr GetChunkIdx(uptr chunk, uptr size) {
    u32 offset = chunk % kRegionSize;
    // Here we divide by a non-constant. This is costly.
    // We require that kRegionSize is at least 2^32 so that offset is 32-bit.
    // We save 2x by using 32-bit div, but may need to use a 256-way switch.
    return offset / (u32)size;
  }

  void PopulateFreeList(uptr class_id, RegionInfo *region) {
    CHECK(region->free_list.empty());
    uptr size = SizeClassMap::Size(class_id);
    uptr beg_idx = region->allocated_user;
    uptr end_idx = beg_idx + kPopulateSize;
    uptr region_beg = kSpaceBeg + kRegionSize * class_id;
    if (end_idx + size > region->mapped_user) {
      // Do the mmap for the user memory.
      uptr map_size = kUserMapSize;
      while (end_idx + size > region->mapped_user + map_size)
        map_size += kUserMapSize;
      CHECK_GE(region->mapped_user + map_size, end_idx);
      MapWithCallback(region_beg + region->mapped_user, map_size);
      region->mapped_user += map_size;
    }
    uptr idx = beg_idx;
    uptr i = 0;
    do {  // do-while loop because we need to put at least one item.
      uptr p = region_beg + idx;
      region->free_list.push_front(reinterpret_cast<AllocatorListNode*>(p));
      idx += size;
      i++;
    } while (idx < end_idx);
    region->allocated_user += idx - beg_idx;
    CHECK_LE(region->allocated_user, region->mapped_user);
    region->allocated_meta += i * kMetadataSize;
    if (region->allocated_meta > region->mapped_meta) {
      uptr map_size = kMetaMapSize;
      while (region->allocated_meta > region->mapped_meta + map_size)
        map_size += kMetaMapSize;
      // Do the mmap for the metadata.
      CHECK_GE(region->mapped_meta + map_size, region->allocated_meta);
      MapWithCallback(region_beg + kRegionSize -
                      region->mapped_meta - map_size, map_size);
      region->mapped_meta += map_size;
    }
    CHECK_LE(region->allocated_meta, region->mapped_meta);
    if (region->allocated_user + region->allocated_meta > kRegionSize) {
      Printf("Out of memory. Dying.\n");
      Printf("The process has exhausted %zuMB for size class %zu.\n",
          kRegionSize / 1024 / 1024, size);
      Die();
    }
  }

  void *AllocateBySizeClass(uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    RegionInfo *region = GetRegionInfo(class_id);
    SpinMutexLock l(&region->mutex);
    if (region->free_list.empty()) {
      PopulateFreeList(class_id, region);
    }
    CHECK(!region->free_list.empty());
    AllocatorListNode *node = region->free_list.front();
    region->free_list.pop_front();
    return reinterpret_cast<void*>(node);
  }

  void DeallocateBySizeClass(void *p, uptr class_id) {
    RegionInfo *region = GetRegionInfo(class_id);
    SpinMutexLock l(&region->mutex);
    region->free_list.push_front(reinterpret_cast<AllocatorListNode*>(p));
  }
};

// SizeClassAllocator32 -- allocator for 32-bit address space.
// This allocator can theoretically be used on 64-bit arch, but there it is less
// efficient than SizeClassAllocator64.
//
// [kSpaceBeg, kSpaceBeg + kSpaceSize) is the range of addresses which can
// be returned by MmapOrDie().
//
// Region:
//   a result of a single call to MmapAlignedOrDie(kRegionSize, kRegionSize).
// Since the regions are aligned by kRegionSize, there are exactly
// kNumPossibleRegions possible regions in the address space and so we keep
// an u8 array possible_regions[kNumPossibleRegions] to store the size classes.
// 0 size class means the region is not used by the allocator.
//
// One Region is used to allocate chunks of a single size class.
// A Region looks like this:
// UserChunk1 .. UserChunkN <gap> MetaChunkN .. MetaChunk1
//
// In order to avoid false sharing the objects of this class should be
// chache-line aligned.
template <const uptr kSpaceBeg, const u64 kSpaceSize,
          const uptr kMetadataSize, class SizeClassMap,
          class MapUnmapCallback = NoOpMapUnmapCallback>
class SizeClassAllocator32 {
 public:
  void Init() {
    state_ = reinterpret_cast<State *>(MapWithCallback(sizeof(State)));
  }

  void *MapWithCallback(uptr size) {
    size = RoundUpTo(size, GetPageSizeCached());
    void *res = MmapOrDie(size, "SizeClassAllocator32");
    MapUnmapCallback().OnMap((uptr)res, size);
    return res;
  }
  void UnmapWithCallback(uptr beg, uptr size) {
    MapUnmapCallback().OnUnmap(beg, size);
    UnmapOrDie(reinterpret_cast<void *>(beg), size);
  }

  bool CanAllocate(uptr size, uptr alignment) {
    return size <= SizeClassMap::kMaxSize &&
      alignment <= SizeClassMap::kMaxSize;
  }

  void *Allocate(uptr size, uptr alignment) {
    if (size < alignment) size = alignment;
    CHECK(CanAllocate(size, alignment));
    return AllocateBySizeClass(ClassID(size));
  }

  void Deallocate(void *p) {
    CHECK(PointerIsMine(p));
    DeallocateBySizeClass(p, GetSizeClass(p));
  }

  void *GetMetaData(void *p) {
    CHECK(PointerIsMine(p));
    uptr mem = reinterpret_cast<uptr>(p);
    uptr beg = ComputeRegionBeg(mem);
    uptr size = SizeClassMap::Size(GetSizeClass(p));
    u32 offset = mem - beg;
    uptr n = offset / (u32)size;  // 32-bit division
    uptr meta = (beg + kRegionSize) - (n + 1) * kMetadataSize;
    return reinterpret_cast<void*>(meta);
  }

  // Allocate several chunks of the given class_id.
  void BulkAllocate(uptr class_id, AllocatorFreeList *free_list) {
    SizeClassInfo *sci = GetSizeClassInfo(class_id);
    SpinMutexLock l(&sci->mutex);
    EnsureSizeClassHasAvailableChunks(sci, class_id);
    CHECK(!sci->free_list.empty());
    BulkMove(SizeClassMap::MaxCached(class_id), &sci->free_list, free_list);
  }

  // Swallow the entire free_list for the given class_id.
  void BulkDeallocate(uptr class_id, AllocatorFreeList *free_list) {
    SizeClassInfo *sci = GetSizeClassInfo(class_id);
    SpinMutexLock l(&sci->mutex);
    sci->free_list.append_front(free_list);
  }

  bool PointerIsMine(void *p) {
    return GetSizeClass(p) != 0;
  }

  uptr GetSizeClass(void *p) {
    return state_->possible_regions[ComputeRegionId(reinterpret_cast<uptr>(p))];
  }

  void *GetBlockBegin(void *p) {
    CHECK(PointerIsMine(p));
    uptr mem = reinterpret_cast<uptr>(p);
    uptr beg = ComputeRegionBeg(mem);
    uptr size = SizeClassMap::Size(GetSizeClass(p));
    u32 offset = mem - beg;
    u32 n = offset / (u32)size;  // 32-bit division
    uptr res = beg + (n * (u32)size);
    return reinterpret_cast<void*>(res);
  }

  uptr GetActuallyAllocatedSize(void *p) {
    CHECK(PointerIsMine(p));
    return SizeClassMap::Size(GetSizeClass(p));
  }

  uptr ClassID(uptr size) { return SizeClassMap::ClassID(size); }

  uptr TotalMemoryUsed() {
    // No need to lock here.
    uptr res = 0;
    for (uptr i = 0; i < kNumPossibleRegions; i++)
      if (state_->possible_regions[i])
        res += kRegionSize;
    return res;
  }

  void TestOnlyUnmap() {
    for (uptr i = 0; i < kNumPossibleRegions; i++)
      if (state_->possible_regions[i])
        UnmapWithCallback((i * kRegionSize), kRegionSize);
    UnmapWithCallback(reinterpret_cast<uptr>(state_), sizeof(State));
  }

  typedef SizeClassMap SizeClassMapT;
  static const uptr kNumClasses = SizeClassMap::kNumClasses;

 private:
  static const uptr kRegionSizeLog = SANITIZER_WORDSIZE == 64 ? 24 : 20;
  static const uptr kRegionSize = 1 << kRegionSizeLog;
  static const uptr kNumPossibleRegions = kSpaceSize / kRegionSize;

  struct SizeClassInfo {
    SpinMutex mutex;
    AllocatorFreeList free_list;
    char padding[kCacheLineSize - sizeof(uptr) - sizeof(AllocatorFreeList)];
  };
  COMPILER_CHECK(sizeof(SizeClassInfo) == kCacheLineSize);

  uptr ComputeRegionId(uptr mem) {
    uptr res = mem >> kRegionSizeLog;
    CHECK_LT(res, kNumPossibleRegions);
    return res;
  }

  uptr ComputeRegionBeg(uptr mem) {
    return mem & ~(kRegionSize - 1);
  }

  uptr AllocateRegion(uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    uptr res = reinterpret_cast<uptr>(MmapAlignedOrDie(kRegionSize, kRegionSize,
                                      "SizeClassAllocator32"));
    MapUnmapCallback().OnMap(res, kRegionSize);
    CHECK_EQ(0U, (res & (kRegionSize - 1)));
    CHECK_EQ(0U, state_->possible_regions[ComputeRegionId(res)]);
    state_->possible_regions[ComputeRegionId(res)] = class_id;
    return res;
  }

  SizeClassInfo *GetSizeClassInfo(uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    return &state_->size_class_info_array[class_id];
  }

  void EnsureSizeClassHasAvailableChunks(SizeClassInfo *sci, uptr class_id) {
    if (!sci->free_list.empty()) return;
    uptr size = SizeClassMap::Size(class_id);
    uptr reg = AllocateRegion(class_id);
    uptr n_chunks = kRegionSize / (size + kMetadataSize);
    for (uptr i = reg; i < reg + n_chunks * size; i += size)
      sci->free_list.push_back(reinterpret_cast<AllocatorListNode*>(i));
  }

  void *AllocateBySizeClass(uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    SizeClassInfo *sci = GetSizeClassInfo(class_id);
    SpinMutexLock l(&sci->mutex);
    EnsureSizeClassHasAvailableChunks(sci, class_id);
    CHECK(!sci->free_list.empty());
    AllocatorListNode *node = sci->free_list.front();
    sci->free_list.pop_front();
    return reinterpret_cast<void*>(node);
  }

  void DeallocateBySizeClass(void *p, uptr class_id) {
    CHECK_LT(class_id, kNumClasses);
    SizeClassInfo *sci = GetSizeClassInfo(class_id);
    SpinMutexLock l(&sci->mutex);
    sci->free_list.push_front(reinterpret_cast<AllocatorListNode*>(p));
  }

  struct State {
    u8 possible_regions[kNumPossibleRegions];
    SizeClassInfo size_class_info_array[kNumClasses];
  };
  State *state_;
};

// Objects of this type should be used as local caches for SizeClassAllocator64.
// Since the typical use of this class is to have one object per thread in TLS,
// is has to be POD.
template<class SizeClassAllocator>
struct SizeClassAllocatorLocalCache {
  typedef SizeClassAllocator Allocator;
  static const uptr kNumClasses = SizeClassAllocator::kNumClasses;
  // Don't need to call Init if the object is a global (i.e. zero-initialized).
  void Init() {
    internal_memset(this, 0, sizeof(*this));
  }

  void *Allocate(SizeClassAllocator *allocator, uptr class_id) {
    CHECK_NE(class_id, 0UL);
    CHECK_LT(class_id, kNumClasses);
    AllocatorFreeList *free_list = &free_lists_[class_id];
    if (free_list->empty())
      allocator->BulkAllocate(class_id, free_list);
    CHECK(!free_list->empty());
    void *res = free_list->front();
    free_list->pop_front();
    return res;
  }

  void Deallocate(SizeClassAllocator *allocator, uptr class_id, void *p) {
    CHECK_NE(class_id, 0UL);
    CHECK_LT(class_id, kNumClasses);
    AllocatorFreeList *free_list = &free_lists_[class_id];
    free_list->push_front(reinterpret_cast<AllocatorListNode*>(p));
    if (free_list->size() >= 2 * SizeClassMap::MaxCached(class_id))
      DrainHalf(allocator, class_id);
  }

  void Drain(SizeClassAllocator *allocator) {
    for (uptr i = 0; i < kNumClasses; i++) {
      allocator->BulkDeallocate(i, &free_lists_[i]);
      CHECK(free_lists_[i].empty());
    }
  }

  // private:
  typedef typename SizeClassAllocator::SizeClassMapT SizeClassMap;
  AllocatorFreeList free_lists_[kNumClasses];

  void DrainHalf(SizeClassAllocator *allocator, uptr class_id) {
    AllocatorFreeList *free_list = &free_lists_[class_id];
    AllocatorFreeList half;
    half.clear();
    const uptr count = free_list->size() / 2;
    for (uptr i = 0; i < count; i++) {
      AllocatorListNode *node = free_list->front();
      free_list->pop_front();
      half.push_front(node);
    }
    allocator->BulkDeallocate(class_id, &half);
  }
};

// This class can (de)allocate only large chunks of memory using mmap/unmap.
// The main purpose of this allocator is to cover large and rare allocation
// sizes not covered by more efficient allocators (e.g. SizeClassAllocator64).
template <class MapUnmapCallback = NoOpMapUnmapCallback>
class LargeMmapAllocator {
 public:
  void Init() {
    internal_memset(this, 0, sizeof(*this));
    page_size_ = GetPageSizeCached();
  }
  void *Allocate(uptr size, uptr alignment) {
    CHECK(IsPowerOfTwo(alignment));
    uptr map_size = RoundUpMapSize(size);
    if (alignment > page_size_)
      map_size += alignment;
    if (map_size < size) return 0;  // Overflow.
    uptr map_beg = reinterpret_cast<uptr>(
        MmapOrDie(map_size, "LargeMmapAllocator"));
    MapUnmapCallback().OnMap(map_beg, map_size);
    uptr map_end = map_beg + map_size;
    uptr res = map_beg + page_size_;
    if (res & (alignment - 1))  // Align.
      res += alignment - (res & (alignment - 1));
    CHECK_EQ(0, res & (alignment - 1));
    CHECK_LE(res + size, map_end);
    Header *h = GetHeader(res);
    h->size = size;
    h->map_beg = map_beg;
    h->map_size = map_size;
    {
      SpinMutexLock l(&mutex_);
      h->next = list_;
      h->prev = 0;
      if (list_)
        list_->prev = h;
      list_ = h;
    }
    return reinterpret_cast<void*>(res);
  }

  void Deallocate(void *p) {
    Header *h = GetHeader(p);
    {
      SpinMutexLock l(&mutex_);
      Header *prev = h->prev;
      Header *next = h->next;
      if (prev)
        prev->next = next;
      if (next)
        next->prev = prev;
      if (h == list_)
        list_ = next;
    }
    MapUnmapCallback().OnUnmap(h->map_beg, h->map_size);
    UnmapOrDie(reinterpret_cast<void*>(h->map_beg), h->map_size);
  }

  uptr TotalMemoryUsed() {
    SpinMutexLock l(&mutex_);
    uptr res = 0;
    for (Header *l = list_; l; l = l->next) {
      res += RoundUpMapSize(l->size);
    }
    return res;
  }

  bool PointerIsMine(void *p) {
    return GetBlockBegin(p) != 0;
  }

  uptr GetActuallyAllocatedSize(void *p) {
    return RoundUpTo(GetHeader(p)->size, page_size_);
  }

  // At least page_size_/2 metadata bytes is available.
  void *GetMetaData(void *p) {
    return GetHeader(p) + 1;
  }

  void *GetBlockBegin(void *ptr) {
    uptr p = reinterpret_cast<uptr>(ptr);
    SpinMutexLock l(&mutex_);
    for (Header *l = list_; l; l = l->next) {
      if (p >= l->map_beg && p < l->map_beg + l->map_size)
        return GetUser(l);
    }
    return 0;
  }

 private:
  struct Header {
    uptr map_beg;
    uptr map_size;
    uptr size;
    Header *next;
    Header *prev;
  };

  Header *GetHeader(uptr p) {
    CHECK_EQ(p % page_size_, 0);
    return reinterpret_cast<Header*>(p - page_size_);
  }
  Header *GetHeader(void *p) { return GetHeader(reinterpret_cast<uptr>(p)); }

  void *GetUser(Header *h) {
    CHECK_EQ((uptr)h % page_size_, 0);
    return reinterpret_cast<void*>(reinterpret_cast<uptr>(h) + page_size_);
  }

  uptr RoundUpMapSize(uptr size) {
    return RoundUpTo(size, page_size_) + page_size_;
  }

  uptr page_size_;
  Header *list_;
  SpinMutex mutex_;
};

// This class implements a complete memory allocator by using two
// internal allocators:
// PrimaryAllocator is efficient, but may not allocate some sizes (alignments).
//  When allocating 2^x bytes it should return 2^x aligned chunk.
// PrimaryAllocator is used via a local AllocatorCache.
// SecondaryAllocator can allocate anything, but is not efficient.
template <class PrimaryAllocator, class AllocatorCache,
          class SecondaryAllocator>  // NOLINT
class CombinedAllocator {
 public:
  void Init() {
    primary_.Init();
    secondary_.Init();
  }

  void *Allocate(AllocatorCache *cache, uptr size, uptr alignment,
                 bool cleared = false) {
    // Returning 0 on malloc(0) may break a lot of code.
    if (size == 0)
      size = 1;
    if (size + alignment < size)
      return 0;
    if (alignment > 8)
      size = RoundUpTo(size, alignment);
    void *res;
    if (primary_.CanAllocate(size, alignment)) {
      if (cache)  // Allocate from cache.
        res = cache->Allocate(&primary_, primary_.ClassID(size));
      else  // No thread-local cache, allocate directly from primary allocator.
        res = primary_.Allocate(size, alignment);
    } else {  // Secondary allocator does not use cache.
      res = secondary_.Allocate(size, alignment);
    }
    if (alignment > 8)
      CHECK_EQ(reinterpret_cast<uptr>(res) & (alignment - 1), 0);
    if (cleared && res)
      internal_memset(res, 0, size);
    return res;
  }

  void Deallocate(AllocatorCache *cache, void *p) {
    if (!p) return;
    if (primary_.PointerIsMine(p))
      cache->Deallocate(&primary_, primary_.GetSizeClass(p), p);
    else
      secondary_.Deallocate(p);
  }

  void *Reallocate(AllocatorCache *cache, void *p, uptr new_size,
                   uptr alignment) {
    if (!p)
      return Allocate(cache, new_size, alignment);
    if (!new_size) {
      Deallocate(cache, p);
      return 0;
    }
    CHECK(PointerIsMine(p));
    uptr old_size = GetActuallyAllocatedSize(p);
    uptr memcpy_size = Min(new_size, old_size);
    void *new_p = Allocate(cache, new_size, alignment);
    if (new_p)
      internal_memcpy(new_p, p, memcpy_size);
    Deallocate(cache, p);
    return new_p;
  }

  bool PointerIsMine(void *p) {
    if (primary_.PointerIsMine(p))
      return true;
    return secondary_.PointerIsMine(p);
  }

  void *GetMetaData(void *p) {
    if (primary_.PointerIsMine(p))
      return primary_.GetMetaData(p);
    return secondary_.GetMetaData(p);
  }

  void *GetBlockBegin(void *p) {
    if (primary_.PointerIsMine(p))
      return primary_.GetBlockBegin(p);
    return secondary_.GetBlockBegin(p);
  }

  uptr GetActuallyAllocatedSize(void *p) {
    if (primary_.PointerIsMine(p))
      return primary_.GetActuallyAllocatedSize(p);
    return secondary_.GetActuallyAllocatedSize(p);
  }

  uptr TotalMemoryUsed() {
    return primary_.TotalMemoryUsed() + secondary_.TotalMemoryUsed();
  }

  void TestOnlyUnmap() { primary_.TestOnlyUnmap(); }

  void SwallowCache(AllocatorCache *cache) {
    cache->Drain(&primary_);
  }

 private:
  PrimaryAllocator primary_;
  SecondaryAllocator secondary_;
};

}  // namespace __sanitizer

#endif  // SANITIZER_ALLOCATOR_H